Catalytic reforming is one of the major processes for petroleum refining, and is a process in which raw oil such as naphtha is transformed into reformate rich in aromatics at specific temperature and pressure in presence of hydrogen and catalyst, and hydrogen gas is obtained as a byproduct. The reformate obtained through gas liquid separation of the mixture produced in catalytic reforming may be directly used as an additive for vehicle fuels; alternatively may be used for producing chemicals such as benzene, methyl benzene, and dimethyl benzene etc through an aromatics extraction process.
Reformate not only is rich in fractions of aromatics and solvent oil, but also contains a few olefins. Therefore, it is necessary to remove the olefins so as to produce qualified products of aromatics and solvent oil. Furthermore, in recent years, as the developing of wide fraction reforming technique and the increasing of the reaction severity, the olefin content in reformate increased accordingly. Therefore, the necessity of removing olefins from reformate is more obvious.
At present, the methods for removing olefins from reformate include clay adsorption refining, and post-hydrogenation for distillate or full range of reformate. For clay adsorption refining, there exist the drawbacks that the adsorptive capacity of clay is limited, and the waste clay can not be regenerated. In recent years, the distillate or full range of reformate is subject to selective hydrogenation in presence of Pd or Pt based noble metal catalysts, so as to remove olefins from reformate.
CN1004421B discloses a hydrorefining method of reformate, in which reformate with a bromine index in a range of 0.5-8 g bromine/100 g and an aromatic content in a range of 35% to 55% by weight is used as the raw material, the reaction is preformed at a temperature in a range of 200° C. to 300° C. and a partial pressure of hydrogen in a range of 5-20 kg/cm2 with a liquid-volume space velocity in a range of 6 h−1 to 20 h−1 and a volume ratio of hydrogen to oil in a range of 200 to 1,000. A thin-shell strip-shaped Pd—Al2O3 catalyst with a Pd content in a range of 0.15% to 0.6% by weight (in relation to the support) is used.
CN1049001C discloses a hydrorefining method of reformate, in which reformate with a bromine index in a range of 0.5-8.0 g bromine/10.0 g is used as the raw material, and the hydrogenation catalyst is thin-shell Pd/γ-Al2O3 with a Pd content in a range of 0.15% to 6% by weight (in relation to the support). Aromatics with carbon number higher than 9 have been removed from the raw material, and the aromatic content is in a range of 20% to 85% by weight. The reaction temperature is in a range of 150° C. to 200° C., the partial pressure of hydrogen in the reactor is in a range of 0.5 MPa to 3.0 MPa, the liquid-volume space velocity is in a range of 3 h−1 to 15 h−1, and the volume ratio of hydrogen to oil is in a range of 100 to 500.
Both of the methods disclosed by CN1004421B and CN1049001C employ a trickle-bed hydrogenation process, a large quantity of circulating hydrogen has to be maintained in the apparatus. As a result, on one hand, a compressor for circulating hydrogen is required; on the other hand, the apparatus is bulky.